I had time to spare so I toyed with the example exercise. Now I am not sure if I misunderstood something because solution is fairly simple using only channels: https://go.dev/play/p/tD8cWdKfkKW
I replied to your comment on my website, but for posterity here, yes, I do think you did a good job for the part about exiting when bestScore > 100. There's nitpicks, but this is fine! It makes sense, and nice use of a select over a send.
I did expect that this exercise would come after the first one though, and doing this on top of a solution to the first exercise is a bit harder. That said, I also don't mean to claim either are impossible. It's just tough to reason about.
Your example solution has only one player. Your solution won't work when there are multiple players.
I don't think you examined the code in full. main spawns 10 go routines that are constantly sending player scores to the game. That means 10 different players are sending their scores concurrently until someone reaches score of 100.